This invention relates to a method and apparatus for detecting misapplied caps on containers. More specifically, this invention relates to a method and apparatus which can be used to detect damaged or misapplied crown caps (usually called "bull nose crowns" in the beverage industry) on beverage and other containers.
Beverage containers, for example, are often sealed under internal pressurization (e.g., beer). If biological contamination or seal failure occurs, the beverage quality may be significantly degraded and may be dangerous to consumers. Even if not resulting in a health hazard, improperly applied caps create the perception of poor quality and can result in lost sales for cosmetic reasons. Accordingly, some manufacturers test the internal pressure/vacuum of containers before shipment to identify and remove defective containers.
Two non-intrusive testing techniques are shown in Hayward, U.S. Pat. No. 3,802,252 and Woringer, U.S. Pat. No. 5,353,631, both of which are assigned to Benthos, Inc., and incorporated herein by reference. Systems of the type described in the foregoing patents have been sold under the name TapTone.RTM. . In such systems, a conductive surface of a closed container is vibrated without contacting it. This is accomplished using a pulsed magnetic field, and the resulting sound is analyzed to determine the pressure in the container. A microphone senses the resulting acoustic energy and converts it into an electrical signal. In the Hayward scheme, analog electronics are used to determine whether the signal has prescribed levels of energy within a pre-tuned frequency band. If a signal is detected within the band, it is inferred that the can is good. In the Woringer scheme, a similar test is performed using digital signal processing (DSP) electronics and software. Bottles displaying abnormal characteristics are ejected from the production line.
U.S. Pat. No. 5,861,548 issued on Jan. 19, 1999 and assigned to the same assignee as the present application, describes a further development on the aforementioned Woringer scheme; the entire disclosure of this patent is herein incorporated by reference. As discussed in '548 patent, closed containers are complex vibratory systems which often exhibit nonlinear effects, and it is not uncommon to find in the use of such systems that the acoustic return signals have been modulated by vibratory modes other than the fundamental mode of the container typically used to predict internal pressure. When such distortions are present, the acoustic signal has been corrupted by misleading information that can lead to false rejections of containers. Accordingly, this patent describes a method in which the original information derived from the detected sound is tested to determine whether a modulating distortion is present therein. If such a modulating distortion is found, its effects are compensated, thereby producing demodulated information. If no modulating distortion is detected, the testing steps of the method (which involve determining whether frequency and amplitude components of the information derived from the detected sound satisfy predetermined spectral frequency and amplitude conditions) are carried out on the original information. If, however, a modulating distortion is detected, the testing steps are carried out on the demodulated information.
The methods and apparatus described in the aforementioned patents have been eminently successful in measuring the pressure of closed containers such as beer bottles traveling at commercial production line speeds, for example, of 1000 bottles per minute or more. However, a serious problem has arisen from the aforementioned misaligned or bull nose crown caps.
Crown caps are installed on-line by high speed capping machines, and when properly applied, should look as shown in FIG. 1 of the accompanying drawings. As shown there, the crown cap (generally designated 10) is applied to a bottle 12 having circular symmetry (e.g., a typical commercial beer bottle), the bottle having at its upper end an essentially cylindrical neck portion 14 having walls defining a circular aperture (not visible in FIG. 1), which is closed by the crown cap 10. The cap 10 has a central circular portion 16, which closes the aperture in the bottle. A skirt 18 may extend outwardly and downwardly from the periphery of the circular portion 16. A plurality of crimped portions 20 are formed in the skirt 18 and serve to grip the neck portion 14, thus securing the cap 10 to the neck portion 14 and sealing the bottle 12. Alternatively, a crown may be applied by twisting on to a bottle, engaging thread on an upper surface.
FIG. 2 shows a misapplied, bull nose crown cap 10'. Essentially, a bull nose crown cap arises when the capping machine displaces the center of the cap from the axis of the bottle, or the cap slides across the neck portion of the bottle during its application. In either case, the end result is that on one side of the cap 10' a portion 22 of the skirt 18' descends lower than usual, while on the opposed side of the cap 10' a portion 24 of the skirt 18' does not extend beyond the periphery of the neck portion 14 of the bottle 12. A bull nose crown may also be a dented crown.
A bull nose cap does not make a gas-tight seal to the bottle and hence the bottle leaks and usually has no internal pressure and should thus be rejected from the bottling line. However, automated detection of bull nose caps is surprisingly difficult. Because of the force applied by commercial high speed capping machines, the central portion of a bull nose cap such as that shown in FIG. 2 is essentially flat and at the same height as the correctly applied cap shown in FIG. 1. Accordingly, a bull nose cap cannot be detected simply by measuring the height of the cap with a photodetector. Also, surprisingly, often bull nose caps, when vibrated by the aforementioned Hayward or Woringer apparatus, emit at essentially the same frequency as a properly installed cap, as shown in FIG. 1. Thus, bull nose caps are a plague to customers and bottlers alike, and it is highly desirable to provide some method for detecting such caps on bottling lines. Accordingly, it is a primary object of the present invention to provide such a method and an apparatus for carrying out this method.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter when the following detailed description is read in conjunction with the drawings.